Waste treatment apparatus and method

ABSTRACT

In apparatus and method for waste treatment by pyrolysis, treated waste is flushed through a grid ( 18 ) to trap recyclable material in the pyrolysis chamber ( 24 ). Pyrolysis is carried out at a temperature of from 400-700° C. and off gases are dissolved in a solution in scrubber ( 13 ) for disposal in a water course. Water is introduced into the chamber as superheated steam via pipes ( 5 ) so as both to flush away treated material and clean the chamber. Recyclable waste is separated from non-recyclable by treating non-recyclable waste by pyrolysis, and flushing treated non-recyclable waste away through liquid exhaust ( 8 ). Apparatus is made as a modular, free-standing unit and comprises plugs for connection to an electricity supply, to a water supply, and to a sewage system ( 16 ) and has a chamber with a volume in the range 0.01-0.5 m 3 .

The present invention relates to waste treatment apparatus and method,in particular apparatus and method for treatment of waste from a rangeof sources, including commercial premises and domestic andmulti-occupancy residences.

Pyrolysis for the disposal of domestic (sanitary) waste is known from WO00/20801. Small pyrolysis units are installed on ships for processingminor quantities of sanitary waste. These units use a multi-stepprocess, requiring a vacuum pump to evacuate air before beginningpyrolysis and to actively evacuate residue from the unit following wastetreatment. In addition to only processing small amounts of homologoussanitary waste the units are situated in close proximity to the user,often within a toilet cubicle.

Large scale industrial pyrolysis of waste is known from inter alia, US2004/0168621, EP 0724008, EP 692677, EP 0505278, and EP 0610120.Industrial size pyrolysis plants require waste to be transported tothem. They operate continuously at high temperatures and due toinstantaneous exposure to these high temperatures and the types of wastethat are processed, these plants tend to produce large quantities ofnoxious gases, including dioxins. These off gases are typically passedto a combustion chamber. Exhaust gases from this chamber are thenoptionally subjected to additional processing before release to theatmosphere, or may be diverted to supply heat within the unit.

Smaller scale pyrolysis is also known from inter alia; JP 2005140346, JP2002081623, JP 2001062437, JP 60105815. EP 1371713, U.S. Pat. No.3,779,182, WO 02/40618, GB 2289324, and GB 2310485.

Pyrolysis Is also known in relation to domestic ovens, for example inthe self cleaning mechanism of US 2005/0145241.

Municipal waste disposal is a growing problem, with the majority of thiswaste being buried in landfill sites. A need to reduce the volume ofwaste for disposal is leading to an increased drive to recycle. Inregard to domestic waste this requires a level of compliance fromresidents and has varying levels of success.

Suitable locations for new landfill sites are relatively uncommon due tostrict hydro-geological requirements, avoidance of water tablecontamination and other environmental considerations. In short, there isan increasing scarcity of suitable waste burial sites and an urgent needfor alternative methods of waste disposal.

Incineration is one of the more widely used alternatives to landfill,however, this requires the production of large scale industrial plants,a time consuming and expensive process. Additionally, public opinion isoften against the building of these plants, particularly on the basis ofobjections to gas release into the local area. The fumes produced bywaste combustion are unavoidable and necessitate the incorporation ofcomplex gas processing mechanisms to remove pollutants.

Waste pyrolysis is an alternative to landfill and incineration, butrequires continuously operating industrial pyrolysis plants. Waste hasto be collected and transported to these plants before being processed.Due to the heterogeneity of waste being processed and the high pyrolytictemperatures toxic emissions are commonly produced. It is not desirableto release these to the atmosphere and thus, as for incineration plants,complex gas processing systems have to be incorporated into plants.

It Is an object of the invention to provide a process and apparatus totreat waste on site on a domestic and large domestic scale. It is anobject of specific embodiments of the invention to do so formulti-occupancy residences and also individual domestic residences andcommercial enterprises such as supermarkets and restaurants. A furtherobject is to reduce and/or remove the need for the transport of wasteand prevent waste ending up as landfill, allowing local authorities tomeet the requirements of recycling directives. A still further object ofthe invention is to enable greater efficiency in collecting recyclablematerials, improving public compliance by facilitating the recyclingprocess.

Accordingly, the invention provides a process for waste treatment andapparatus for carrying out waste treatment by a combination of pyrolysisand combustion steps, the process and apparatus incorporating one ormore, in any and all combinations, or all of the aspects of theinvention described herein.

A first aspect of the invention comprises a process for waste treatmentby pyrolysis and combustion, wherein treated waste is flushed through agrid to trap recyclable material. Apparatus of this aspect comprises apyrolysis chamber having a grid between a waste treatment zone and anexit from the chamber.

A second aspect of the invention comprises pyrolysis of waste at atemperature of from 400-700° C.

A third aspect of the invention comprises dissolving off-gases generatedby pyrolysis and combustion in a solution and disposing of the solution,for example in a sewer. Apparatus of this aspect comprises a tankcontaining a gas treatment solution, an exhaust port for exit of gasesfrom the pyrolysis chamber and a conduit arranged in combination withthe tank such that the gases exiting the chamber are dissolved in thesolution, which can then be disposed of.

A fourth aspect of the invention comprises introducing water into thechamber as superheated steam so as both to flush away treated materialand clean the chamber. Apparatus for this aspect comprises pipework inwalls of the chamber via which in use water enters the chamber, thewater being heated by the hot chamber walls and entering the chamber assuperheated steam.

A fifth aspect of the invention provides for separation of recyclablewaste from non-recyclable waste in mixed waste comprising treatingnon-recyclable waste in the mixed waste by pyrolysis and combustion, andflushing treated non-recyclable waste away whilst retaining recyclablewaste.

A sixth aspect of the invention is a modular pyrolysis and combustionapparatus, which is free-standing and comprises plugs for connection toan electricity supply, to a water supply, and to a sewerage system.

A seventh aspect of the invention is a pyrolysis and combustionapparatus having a chamber with a volume in the range from 0.01-0.5 m³.

In more detail, a first aspect of the invention provides a process forwaste treatment comprising introducing waste into a chamber, heating thewaste to an elevated temperature to effect pyrolysis of the waste,introducing oxygen into the chamber to effect combustion of the waste,and flushing the combusted waste from the chamber with water, whereinthe combusted waste is flushed through a grid to trap recyclablematerial. Treated waste is mostly fine ash and is easily washed throughthe grid and away into e.g. a sewer or other water course. Waste is thustreated on site.

The grid can be located outside the chamber, for example between an exitfrom the chamber and an entrance into the water course. But, it ispreferably located in the chamber, conveniently forming a or part of ashelf, and the method can comprise placing waste introduced into thechamber on the grid.

The method enables separation of recyclable waste, and can thereforecomprise transferring recyclable material from the grid to a receptacleoutside the chamber. Collected recyclable material can be taken away forrecycling—again, avoiding unnecessary land-fill use. The term“recyclable waste” herein refers to commonly recyclable materials thatare not reduced to ash following a waste treatment cycle of theinvention; typically these materials are metal and glass.

The grid is hence preferably moveable, and the method preferablycomprises moving the grid between a first position in which the gridtraps the recyclable material and a second position in which therecyclable material can be transferred into a receptacle. The grid canthus easily, and optionally automatically, be emptied, whether once apyrolysis cycle or after several cycles of waste treatment. For operatorconvenience, the grid may be operated via a control system, such as oneassociated with automatic monitoring and operation of the apparatus.

In a further embodiment, the method comprises agitating the grid duringpyrolysis of the waste. This can assist transfer of heat into the middleof the waste and thus assist more complete pyrolysis of all waste in thechamber.

Pyrolysis and combustion apparatus of this aspect comprises a sealablechamber, a waste treatment zone in the chamber, a port for introducingwaste into the 16 chamber, a port for the exit of treated waste, aheating element, and a grid between the waste treatment zone and theexit port. In use, non-treated material, which generally contains a highproportion of recyclable material, such as glass and metal, is caughtand not flushed away but can instead be recycled.

Suitably, the grid forms a shelf across the chamber to support the wastebeing treated. The grid can also be or be part of a basket in thechamber. The grid can thus be used to locate and/or hold waste in thetreatment zone during pyrolysis. In an apparatus described in moredetail below, the grid forms a shelf towards the bottom of the chamberand a little raised from the floor of the chamber. Waste lies on and issupported by the shelf. After treatment by pyrolysis and combustionwater flushes the resultant ash through the grid onto the floor and thenout of the chamber, large particles typically of undegraded material,being trapped. The floor is generally angled down towards a valved exitport where water exits the chamber.

The grid is preferably moveable between a first position in which ittraps undegraded material during flushing of the chamber and a secondposition in which the undegraded material can be transferred to areceptacle outside the chamber. This facilitates emptying of therecyclables from the chamber.

A control apparatus for moving the grid between the first and secondpositions and a mechanism for agitation of the grid can be associatedwith the grid.

A purpose of the grid is to trap particulate material and not allow thisinto the water course, whilst allowing the ash residue to be easilyflushed away. To this end, the grid may comprise a plurality ofapertures sized 15 mm or less in diameter, 10 mm or less in diameter, 7mm or less in diameter or 5 mm or less in diameter. In a particularembodiment, the grid comprises a plurality of apertures sized about 3 mmin diameter. Generally the apertures can be of any shape, though roundor square apertures are more typical. The grid apertures should not beso fine that they are clogged in use by the ash residue of the wastetreatment cycle, and so are preferably at least 1 mm, more preferably atleast 2 mm in diameter.

The apparatus can also comprise a combination of two or more grids. Forexample, there may be a first grid having a plurality of apertures of afirst size, and a second grid between the first grid and the exit portand having a plurality of apertures of a second size, wherein the firstsize is bigger than the second size. This second, smaller aperture grid,with apertures typically 2 mm or more, or 3 mm or more smaller thanthose of the first, and located closer to the exit of the chamberseparates trapped material into two divisions by size and can prevent orreduce the clogging when there is just one. Suitable aperturecombinations are first grid—15 mm or less, second grid—10 mm or less,preferably 7 mm or less, or first grid—12 mm or less, second grid—10 mmor less, preferably 7 mm or less, or first grid—12 mm or less, secondgrid—7 mm or less, preferably 5 mm or less.

The grid may also be or form part of a basket within the chamber andpreferably removable from the chamber. In use, waste is convenientlyplaced in the basket outside the chamber and the basket, now holding thewaste, placed into the chamber to be treated.

A process for waste treatment in accordance with a second aspect of theinvention comprises introducing waste into a chamber, heating the wasteto an elevated temperature to effect pyrolysis of the waste, introducingoxygen into the chamber to effect combustion of the waste, and flushingthe combusted waste from the chamber with water, wherein the elevatedtemperature to effect pyrolysis is from 400-700° C. Operating at thesetemperatures with rapid cooling of the chamber and its contents oncetreatment is finished and using a relatively short treatment cycle timetends to avoid formation of some of the more noxious contaminantsassociated with standard pyrolysis units or form them to a lesserdegree, whilst ensuring that substantially all waste, other thanrecyclable components, can be treated. Hence an advantage of theinvention is that scrubbing of off gases can be carried out with reducedon-site emissions, and a particularly preferred embodiment of theinvention can be operated with substantially zero emissions on site—offgases being vented away from the apparatus, e.g. via vents in the sewersystem.

The pyrolysis temperature is preferably from 500-700° C., morepreferably from 500-600° C. In a specific embodiment of the process,described in more detail below, the system operates at about 550′C.

It Is further preferred that combustion is carried out at elevatedtemperatures, typically 400° C. or higher, preferably at least 450° C.more preferably at least 500° C. In typical operation of an apparatus ofthe invention, the chamber is heated to the pyrolysis temperature andthen combustion is carried out as the next step without specificseparate heating or cooling of the chamber. Heat generated by combustiongenerally maintains an elevated temperature within the waste anddepending upon its calorific content may slightly increase thetemperature so chamber heaters are generally turned off duringcombustion. Heat can be removed from the chamber by passing off gasesthrough a radiator or a heat exchanger and recovered heat can be usedfor other purposes. Chamber temperature can also be controlled bycontrolling flow of air into the chamber.

Generally chamber temperature during combustion does not rise above 800°C. and preferably not above 750° C. or 700° C.

In a particular embodiment of the invention comprising a large chambervolume an air circulation device, preferably comprising a fan, isincluded to disperse the warm air evenly throughout the chamber as thechamber is being heated in preparation for pyrolysis. Air can be heatedor reheated by heaters in the circulation path. This ensures that theheat is directed into the waste load more effectively—thus speeding upits degradation during pyrolysis. Air circulation may continue duringpyrolysis and/or combustion phases. In smaller chambers the reducedwaste load tends to allow heat to penetrate sufficiently rapidly withoutthe need for air circulation.

The duration of the pyrolysis phase varies according to waste volume,with a limit dictated by chamber volume. Apparatus of the invention aregenerally designed for use in domestic and multi-occupancy residencesand small commercial premises. Waste generally enters the chamber atambient temperature, the chamber is then sealed and the heaters areactivated to heat the chamber to the operating temperature. In apparatusmade and tested to date, this heating phase typically takes 2-20minutes, preferably 5-10 minutes, being dependent on the operatingtemperature required, the chamber volume, and volume of waste in thechamber. In use, it is found that off-gases can evolve in fractions asthe temperature increases and this is believed to result in reducedproduction of certain toxic components, notably dioxins and fluorinscompared to industrial pyrolysis. Processes carried out in suchapparatus generally comprise holding the waste at the elevatedtemperature for 10-90 minutes, preferably for 20-60 minutes. In aspecific embodiment of the process, described in more detail below, thepyrolysis phase has a roughly 30 minute duration.

In some embodiments of the invention intelligent timing systems are usedto control the length of the cycle. These systems can monitor thetemperature of the off-gases being produced and adjust the cycleduration accordingly. Use of these systems improves the power efficiencyof the process. In one example, a control system monitors thetemperature of the off-gases or of the load, such as via a thermocouplelocated proximal to the waste in the chamber, and triggers commencementof combustion once a predetermined temperature (say, about 450° C.-500°C.) is reached. In another example, a control system monitors thetemperature of the off gases from the chamber and when the temperaturehas dropped to a pre-determined level (say 300° C.-400° C.) initiatesthe end of the combustion and the beginning of cooling and cleaning ofthe chamber by introduction of water (as superheated steam). Anotheroption is to monitor the rate of cooling of the chamber, and once thisreaches or approaches the natural cooling rate of the chamber, theninitiate the end of combustion.

In an example of the invention operating in situ, the apparatus is setup with a pre-programmed pyrolysis phase, based on the chamber volumeand anticipated nature of the waste to be processed. The phase may beset up such that the elevated temperature is held for the duration ofthe pyrolysis phase and such that 50% or more of the waste is degraded,preferably 70% or more, more preferably 80% or more. In practice it isproblematic and energy inefficient to ensure 100% treatment, especiallywhen recyclable material is present such as metals and glass, whichwould not be degraded and which can be extracted for recycling. Fromexpected waste volume and content the system may be set up for a givenproperty so that from 60%-95% of waste by weight is pyrolysed.

In a third aspect of the invention a process for waste treatmentcomprises introducing waste into a chamber, heating the waste to anelevated temperature to effect pyrolysis of the waste, introducingoxygen into the chamber to effect combustion of the waste, flushing thecombusted waste from the chamber with water, dissolving gases generatedby the pyrolysis and/or combustion in solution, and disposing of thesolution. Hence, rather than emit these gases or subject them totreatment by combustion the gases are dissolved.

A disadvantage of known pyrolysis plants and incinerators is thegeneration of dioxins and fluorins by initial phases of waste treatment,dealt with by combustion of off-gases, generating intense heat. Planningobjections on environmental grounds' are raised due to the risk thatinadequate combustion will release toxic chemicals into the atmosphere.In the present invention it is found that levels of dioxins, florins andother contaminants, carried away in the water flushed through thechamber are acceptably low and so low as not to pose environmentalproblems, or at least fewer than when such components are combusted.Disposal in a water course is easy and not unsightly and does notrelease contaminants into the immediate vicinity of the pyrolysis plant.The solution can be discharged into the sewerage system.

In use of a specific embodiment of the invention far fewer noxious gasesare produced than would usually be expected following pyrolysis and/orcombustion. Factors Implicated in this unexpected result are believed tobe related to the indirect heating of the waste from an ambienttemperature (below 100° C.) combined with the relatively low maximumtemperature and rapid cooling phase.

Waste gases produced by pyrolysis and/or combustion are suitably passedthrough an aqueous agitation system, to assist dissolution of gases.Gases can be bubbled through the solution, optionally containingsoftened water and optionally containing additives to promotedissolution of the gases.

Not all gases may be dissolved in the solution and it is preferred thatgases are subsequently filtered within a gas cleaning chamber. Themethod also may comprise discharging undissolved gases into the sewagesystem. Hence, in an embodiment, filtered exhaust gases that have notbeen dissolved in solution or retained within the filter are dischargedinto the sewer. These gases then pass up the soil pipe to vent throughventing stacks. The filtered exhaust produced is substantiallycolourless and odourless, principally consisting of carbon dioxide andcarbon monoxide for example.

In preferred embodiments, all of the by-products of the process aredisposed of into the sewer.

A further but associated process of the invention, for waste treatmentin a cycle, comprises providing fresh solution for dissolving gasesgenerated by pyrolysis and/or combustion, carrying out a waste treatmentprocess according to the invention, including dissolving off-gases inthe solution and disposing of the now used solution, and repeating thecycle. The process may include monitoring generation of waste gaseswithin the chamber and triggering flushing combusted material from thechamber after the generation of waste gases has fallen below apredetermined temperature. Evolution of gases diminishes as the processapproaches completion, so monitoring gases is an efficient means oftracking when there is little waste left to be treated.

A pyrolysis apparatus of this aspect comprises a sealable chamber, awaste treatment zone in the chamber, a port for introducing waste intothe chamber, a port for the exit of treated waste, and a heatingelement, the apparatus further comprising a tank to contain a gastreatment solution, an exhaust port for exit of gases from the chamberand a conduit arranged in combination with the tank and the exhaust portsuch that the gases exiting the chamber are contacted with and can bedissolved in the solution.

In an embodiment of the invention set out below, the conduit bubbles thegases through the solution. Another arrangement is for the gases to passthrough an atmosphere saturated with vapour from the solution or forgases to be combined with droplets of the solution, for example bypassing the gases through a spray of the solution. Solution containingdissolved gases is returned to or retained within the tank, which can beemptied as part of a cycle or separately.

A gas cleaning chamber comprising a filter for filtration of gases notdissolved in the solution is optionally downstream of the conduit. Thegas filter used in an example comprises carbon granules, and the filteris suitably removable, for example to enable washing and reuse.Preferably the filter is a ceramic filter. Typically the filter ischanged annually. Used filters can be disposed of via a specialistlandfill site.

A fourth aspect of the invention provides a process for waste treatmentcomprising introducing waste into a chamber, heating the waste to anelevated temperature to effect pyrolysis of the waste, introducingoxygen into the chamber to effect combustion of the waste, and flushingthe combusted waste from the chamber with water, wherein the water isintroduced into the chamber as superheated steam.

In use, the steam cools and cleans the chamber and flushes away the ashresidue of treated material. This is convenient and efficient. Thechamber is left looking clean and hence more acceptable for users. Thereis reduced risk of residue in the chamber which is unsightly or hasunpleasant odour.

To carry out the flushing, water can be introduced into the chamber viapiping in walls of the chamber, the water being heated to formsuperheated steam as it passes through the piping. In this way the wateris heated to the desired temperature by the chamber heat. Also, thechamber is cooled in readiness for a next cycle of use.

The combustion phase includes a step of allowing access of oxygen tomaterial in the chamber, typically supplied as air. The processpreferably comprises introducing oxygen into the chamber via piping inwalls of the chamber and subsequently introducing water into the chambervia the same piping. This efficiently uses common piping, simplifyingsystem design. Piping can be in the walls, outside the walls or in thechamber. The pipe work for the introduction of oxygen (in air) and,later water, to the chamber generally has a diameter in the range of3-15 mm, more preferably from 5-8 mm.

A large volume of steam is generated from a small volume of water, sothe process is efficient compared to use of water only for the flushing.The chamber may thus be flushed with a volume of water which is 50% orless of the volume of the chamber, preferably 35% or less of the volumeof the chamber.

In an example set out below, the process comprises introducing thesuperheated steam into the chamber through a nozzle which directs thesteam at the combusted waste. This can help break down the structure ofthe residue and aid flushing of the chamber.

The process can also or separately comprise introducing the steam intothe chamber via a nozzle which directs the steam at the walls of thechamber. This can help clean chamber walls and aid flushing.

In a preferred arrangement, the process comprises introducing the steaminto the chamber via a plurality of nozzles directed, inter alia, at thecombusted material (i.e. towards the position in the chamber where thematerial is expected to be) and at the walls of the chamber. The steamis preferably introduced into the chamber via a moveable jet.

Apparatus of this aspect comprises a sealable chamber, a waste treatmentzone in the chamber, a port for introducing waste into the chamber, aport for the exit of treated waste, a heating element, a water tank, anda conduit between the water tank and the chamber passing via pipework inwalls of the chamber so that in use water entering the chamber is heatedby the chamber walls and enters the chamber as superheated steam.

One or more nozzles, preferably fixed, may be provided for direction ofthe steam entering the chamber.

An oxygen supply (generally as air) is preferably linked by piping tothe chamber and arranged such that in use oxygen is supplied to thechamber via the piping, and, subsequently, water is supplied to thechamber via the same piping. Flow rates vary with factors includingchamber size and we have operated embodiments with air flow rates offrom 25-200 litres/min.

A fifth aspect of the invention provides a process for separation ofrecyclable waste from non-recyclable waste in mixed waste comprisingintroducing the mixed waste into a chamber, heating the mixed waste toan elevated temperature to effect pyrolysis of the non-recyclable waste,introducing oxygen into the chamber to effect combustion of thenon-recyclable waste, flushing the combusted waste from the chamber withwater whilst retaining the recyclable waste in the chamber, andtransferring the retained recyclable waste to a separate container.

A sixth aspect of the invention provides a modular pyrolysis andcombustion apparatus comprising a sealable chamber, a waste treatmentzone. In the chamber, a port for introducing waste into the chamber, aport for the exit of treated waste, and a heating element, wherein theapparatus is free-standing and comprises plugs for connection to anelectricity supply, to a water supply, and to a sewerage system.

An apparatus for domestic or small business use may comprise a plug forconnection to a mains electricity supply. Bigger apparatus may connectto a 3-phase supply.

A water softening unit is generally part of the apparatus, as areretractable wheels for ease of installation and removal.

A seventh aspect of the invention provides a pyrolysis apparatuscomprising a sealable chamber, a waste treatment zone in the chamber, aport for introducing waste into the chamber, a port for the exit oftreated waste, and a heating element, wherein the chamber volume is inthe range from 0.01-0.50 m³.

The chamber volume is preferably in the range from 0.02-0.30 m³, morepreferably from 0.03-0.20 m³ or from 0.04-0.10 m³. Chambers with volumesof about 0.08 m³ and about 0.14 m³ have been successfully tested todate.

In embodiments of the invention, two or more aspects of the inventionare combined in a particular process or apparatus. Very preferredmethods comprise methods of all aspects of the invention and verypreferred apparatus comprise apparatus of all aspects of the invention.

An apparatus of the invention for use in multi-occupancy dwellingscomprises a sealable destruction chamber, the walls of which are formedof heat resistant materials, for example, of stainless steel and mayinclude: a heating element, generally of an ohmic type; a reflectivelayer (to reflect heat towards the core of the chamber): an insulationlayer; and a water jacket (to cool the outside surface). The chamberitself normally contains a safety system, such as pressure releasevalves, to operate in the event of the internal pressure breaching apredetermined threshold. The chamber is typically rounded, and may becircular or oval in shape.

The lid of the chamber is preferably heavily insulated and usually formsan airtight boundary with the chamber. Typically this is achievedthrough the use of seals which can be formed of a rubber material andthe lid may contain a cooling system for the protection of these seals.

The chamber of one embodiment has an approximately 500 mm diameter witha depth of approximately 650 mm giving a capacity of approximately 130litres (0.13 m³); this will accommodate 2 or 3 white rubbish sacks. Aschamber size and/or percent fill increases, effective transfer of heatto the core of the chamber becomes compromised; optionally the contentsare agitated to ensure effective dissipation of heat.

This apparatus is suitable for multi-occupancy residences and generallyrequires a 3 phase electricity supply. In a smaller domestic setting asmaller chamber uses less power and so 3 KW heating elements aresufficient.

An output from the chamber is normally connected to the sewer, typicallyvia a valved pipe, preferably of a 75-100 mm diameter. The valve isplaced at some distance from the destruction chamber to prevent exposureto high temperatures e.g. greater than 100° C. A separate pipe connectsthe destruction chamber via a radiator or heat exchanger to acombination of one or more gas scrubbing and gas cleaning chambers.These preferably utilise softened tap water in a closed cycle andtypically vent gases to the atmosphere via a sewer connection,downstream of the aforementioned valve. The gas scrubbing chambertypically uses about 4 litres of water and is usually refilled withclean water before each pyrolysis cycle. The primary function of theradiator is to cool off-gases prior to scrubbing and filtration. Theradiator facilitates heat loss from the passing gases such that they arecooled from approximately 600° C. to 200° C., and are preferably cooledto below 100° C. The radiator can be used to recycle heat for otherpurposes, such as to heat water for domestic washing or heating.

The gas scrubbing and gas cleaning chambers control two phases of gasoutput. Preferably gas scrubbing is the first phase, comprising a wateragitation system which causes gas contaminants to dissolve intosolution. Preferably gas cleaning is the second phase, utilising acarbon filter containing carbon granules. Generally this filter isremovable; it may be washed and reused at intervals. More preferably aceramic filter, with or without coating, is used. This can be changedannually.

The process works at elevated temperatures to enable pyrolysis, thesetypically range from 400-700° C., more typically from 500-600° C., andin a specific embodiment the invention operates at about 550° C. Thistemperature is found to enable structural breakdown of the contents.Lower temperatures may result in incomplete breakdown of certain wasteproducts such as bone, while higher temperatures may produce morenoxious gases and lead to problems with emissions or the materials usedfor the structure of the machine.

An option, especially when the load has a relatively high moisturecontent, is to add an extra initial step of maintaining the load at atemperature at about 100° C. to drive off the excess water. Thus, theheaters can be maintained at, say, about 150° C.-200° C. and thetemperature of the chamber monitored. Once the temperature begins torise above 100° C., Indicating that the moisture content is reduced to aconsiderably lower level, the heaters can then be increased e.g. to 500°C.

Water Is Introduced into the chamber following the combustion phase, andis preferably softened tap water; this prevents the build up of limescale deposits. The resulting hot water may be discharged to the sewer,diverted into a domestic heating system or used to preheat the nextload. Further optionally water may be diverted from the outer waterjacket to the destruction chamber following pyrolysis.

In a typical operation of the apparatus, waste enters the destructionchamber and the lid is sealed, the chamber is then heated, to about 550°C. The off-gases produced during pyrolysis are monitored; as waste isdestroyed the levels of these gases reduce, once they drop below apredetermined threshold the heaters are switched off. Air is then passedthrough the heating coil and admitted into the chamber, this is atapproximately 500° C.+ on entry. Entry of the air initiates combustionof the residual waste within the destruction chamber. No external heatis applied at this stage but the heat from the pyrolysis stage isretained. The incoming airflow is maintained at approximately 100litres/min, as higher flow rates may cause the chamber temperature torise unacceptably. Gas output is monitored during combustion, and whilewaste is present the chamber output exceeds the air input. When the gasoutput drops below a set threshold the airflow is shut off and 6-7litres of water are introduced through the pipe system. More water maybe required for larger loads. The water enters the chamber atapproximately 500° C.+ as superheated steam and Inconel™ pipe work isused within the machine in order to withstand the thermal shock of thisprocess. Entry of the superheated steam results in a rush of gas, so thesewer connection is opened immediately prior to introduction of thesteam. The steam cleans the inside of the chamber and washes the ashproducts into the sewer. Non-combusted material is retained by the metalgrid, this can be removed for recycling or left in the machine foranother cycle(s). Some pyrolyzable material may require two or threecycles before it is completely destroyed. Approximately 1 minute afterthe introduction of the steam the internal temperature of thedestruction chamber has reduced to below 100° C. and the lid can besafely opened and the apparatus used again.

Unpyrolysed waste may be retained in the destruction chamber followingcompletion of the pyrolysis cycle due to the location of one or moregrids in front of the chamber output. In use, glass and/or metal in thewaste is not destroyed by the pyrolysis and after the chamber is flushedwith steam/water the glass and/or metal is captured in the grid. Thegrid apertures are designed to allow ash from treated waste to passthrough and so are generally at least 1 mm in diameter; In more detail,the apertures are generally approximately square or approximately 16circular with dimensions of about 10 mm×10 mm if square or having adiameter of 10 mm if round, or less, preferably being about 7 mm×7 mm orabout 7 mm in diameter, or less, more preferably about 5 mm×5 mm orabout 5 mm in diameter or less. In a specific embodiment, grid aperturesof dimension about 3 mm×3 mm have been used. Said grids may be removedfrom the machine on completion of a pyrolysis cycle to transferunprocessed material to a separate receptacle, and this removal may becarried out manually or as part of an automated process.

The apparatus can suitably be adaptable to fit existing facilities inbuildings and it may prove desirable to limit (the size of) objects thatcan enter the system. Accordingly the apparatus may include a feedingdevice to restrict the dimensions of material that can be introduced tothe system. Optionally, the invention may include an apparatus toagitate the contents of the destruction chamber during pyrolysis inorder to aid effective heat distribution. Further optionally, theinvention may include a mechanism to prevent or mitigate the directimpact of waste into the destruction chamber.

Waste production/disposal is known to be intermittent; it is desirablefor the invention to be able to effectively manage ‘busy’ and ‘quiet’times. Accordingly the invention may include an apparatus to controlwaste input, preferably this is in the form of a buffer storage system,and optionally this may comprise a storage hopper and/or conveyor belt.

An apparatus of the invention is used for destruction of waste in amulti-occupancy dwelling. This invention removes the need for thetransport of waste from the site of production to sites ofdestruction/disposal. It further reduces the demand on landfill sitesand allows local authorities to comply with impending Europeandirectives on waste disposal.

The Invention can provide a method of low gaseous emission pyrolysis.Due to the gradual (rather than instantaneous) exposure of the load toheat, the waste content and the comparatively low temperatures requiredfor pyrolysis of this waste, fewer noxious chemicals are produced incomparison to industrial scale pyrolysis. Those dioxins and fluorinswhich are produced during pyrolysis are relatively water soluble andthus, following gas processing, are at acceptable levels for disposalvia the sewer.

The pyrolysis system can be adapted according to the individualcustomer, the type and amount of waste dictate the required size of theunit and the temperatures needed. In an example described below theapparatus and process are controlled by a programmable logic controller.Preferably, subsequent embodiments of the invention will utilise amicroprocessor for this action, as this will reduce production costs.

The invention is now illustrated in the following specific embodimentwith reference to the accompanying drawings in which:—

FIG. 1 shows a schematic cross-sectional view of a pyrolysis apparatus;and

FIG. 2 shows schematic isometric view of the apparatus.

Referring to the drawings, a pyrolysis apparatus has the followingfeatures:—

PARTS LIST AND KEY

-   -   1. Storage Chute    -   2. Loading Door Mechanism    -   3. Loading Door    -   4. Lid    -   5. Air/water tubes    -   6. Heating Plates    -   7. Access Drawer    -   8. Chamber Exhaust (liquid)    -   9. Gas Exhaust Control Valve    -   10. Gas Cooling Radiator    -   11. Liquid Bleed Valve    -   12. Liquid Exhaust Control Valve    -   13. Wet Scrubber    -   14. Filtration System    -   15. Filtration Return-Protection Valve    -   16. Exit to Foul Water    -   17. Cage    -   18. Mesh    -   19. Treatment zone    -   20. Hinges    -   21. Exit Port for Liquid    -   22. Exit Port for Gas    -   23. Access Door to Cage    -   24. Chamber    -   25. Sealing Plate    -   Loading Sensor (not shown)    -   Seals (not shown)    -   Lid Cooler (not shown)    -   Insulation for chamber (not shown)    -   Water Jacket on Chamber (not shown)    -   Air Compressor (not shown)    -   Air tank (not shown)    -   Water Pump (not shown)    -   Water Header Tank (not shown)    -   Gas Flare (not shown)

Main Components: Heating Chamber

The chamber (24) is manufactured from stainless steel (AusteniticChromium-Nickel Steel) grade 316. Other materials, e.g. titanium, can beused. The weld material used in fabrication retains the corrosionresistant properties of the main body of the chamber. The chamber isresilient to the frequent heating/cooling cycles, and the materialrequires a heat treatment and finishing process within its manufacture.

The chamber has dimensions of 450×450×700 mm, with a wall thickness of1:5 mm (the walls can also be up to 4 mm thick). On the top face of thechamber is a flat sealing plate (25) which is ground to a flat surface(+/−0.1 mm max) across the top surface. The chamber also features twooutlets, an exit port (21) leading to an exhaust (8) at the base forliquid waste (approx 60 mm dia) and an exit port or outlet (22) at thetop of one of the sides for the gas and vapour (approx 38 mm dia).

Lid

The lid (4) is manufactured from a similar material as the heatingchamber, although it is manufactured from a flat plate. The surface isfinished so the lid and chamber form a critical sealing surface. The lidis also reinforced on its rear to avoid any warping or distortion due torepetitive heating and cooling cycles. The lid is designed to be asrobust as possible. The lid houses the hinge mechanism (20) on its rearand gives a mating surface for sealing on its underside. The lid alsocontains the seals (discussed below). The lid features an integratedwater cooling surface (not shown) which runs around the rim of the lid,directly above the seals. This prolongs the product life cycle.

Seals

PTFE coated silicone rubber seals (not shown) are used to seal anynon-permanent mating faces, such as the chamber lid and access drawer.All other mating surfaces feature a soft metal gasket arrangement.

Access Drawer

The drawer (7) is used to remove any incompatible materials that havenot been decomposed by the process. The drawer features a water coolingcircuit (not shown) similar to the lid that is used to cool the matingsurfaces of the seal. The working surface of the drawer is a fine mesh(18) of a 3 mm aperture (up to a 5 mm aperture can also be used) whichallows movement of solids, liquids and gases in the system. The draweralso features a sensor that informs the operator that the drawer hasreached a certain predetermined capacity, and requires emptying.

Heating Elements

Flat plate heaters (6) are used on all four vertical sides of thechamber. The heaters are assembled to give maximum contact with theoutside of the chamber.

Air/Water Tubes

The tubes (5) are used to pass water and air around the outer surfacesof the chamber. This is performed to preheat the waste prior to directinjection of the superheated air and steam at the latter phases of theprocess. The tubes are manufactured from Stainless Steel material(Inconel™ material can also be used), of 5 mm diameter.

Heat Insulation

On the outside of the heaters are many efficient insulating layers (notshown) which work to both reflect heat back into the chamber and reduceheat emissions to the outer surfaces of the assembly. This insulationensures that all heating energy is used in a useful way to directly heatthe waste product.

On the underside of the lid is a layer of ceramic plate (not shown) (5mm thick) which is bonded onto the stainless steel lid. This reducesexternal heat loss and increases the product lifespan of seals etc.

Cooling Radiator

The radiator's primary function is to cool the gas which has beenemitted from the product, prior to any filtration. The cooling prolongsthe life and retains maximum efficiency of the filtration equipment.

The radiator (10) consists of a 38 mm tube (or same diameter as thechamber gas exhaust), which is bent in 2 axes. Fine horizontal fins arewelded to the outside of the tube to increase heat loss of the passinggases. This reduces the exhaust gases from temperatures in the region of600° C. down to 200° C. or below.

Wet Scrubber

The wet scrubber (13) is placed after the gas radiator in the system andremoves particulate matter from the passing gases and dissolves gases inthe scrubbing liquid for disposal subsequently. Inside the scrubbingdevice is a series of stacked jets producing a very fine mist of water.The mist attracts particulates to the outer surfaces of the mistdroplets, and these are ‘pulled out’ of the gas flow and into the liquidwaste stream. Within the scrubber is a series of openings which guidethe flow of the waste gases directly past the mist jets.

Purification Systems

A ceramic filter (14) is preferably used. This cleans the exhaust gasesprior to release to the foul water system. The filter screws onto afixed manifold having a rubber seal which mates onto the manifold. Gasespass into the centre of the filter via a tube with an external threadwhich secures the filter to the manifold. The gases pass through theporous membrane of the filter and through to the return tube in themanifold. In normal use, the filter is replaced approximately everyyear. In alternative embodiments an active carbon filter is used, thisis replaced approximately every 90 days.

Waste Gas Flare

After the purification systems there is optionally a small gas flareoutlet to burn off any flammable gas by-products from the waste. Theflare is sited and specified so that it does not compromise safe andsecure operation of the unit. However, in preferred embodiments a wastegas flare is not required due to the combination of low processingtemperatures and gas cleaning systems.

Other Key Components: Loading Chute

The chute (1) is fabricated from a corrosion resistant material. It hasa storage capacity less than the chamber, eliminating the possibility ofoverloading.

There is a sensor (not shown) within the chamber which records the levelthat the waste has been loaded to, and when this level has been reacheda separate solenoid/mechanism arrangement (not shown) locks off accessto the system via the external chute. The chute also features an accessdoor (not shown) which allows an operator to manually load the system ondemand.

Cage

The system is housed within a cage (17). The framework has castors (notshown) to allow the unit to be removed easily due to a breakdown etc.The cage also has fixed outlets (not shown) for all services needed—foulwater, fresh water and 3 phase (single phase may be used if feasible)electricity. Services are simply plugged in and are easily disconnected.

There Is a lockable front access door (23) which allows an operator toperform basic maintenance tasks. The cage also protects equipment fromvandalism.

Chamber Water Jacket

On the outside of the chamber and lid insulation there is a water jacket(not shown). This ensures that the insulation and chamber do notoverheat and it gives the system the ability to cool rapidly on demand.

Control Electronics

A programmable logic controller (PLC) (not shown) controls the operationof the system, and monitor sensors (not shown) that are positionedthroughout most mechanisms and active components within the system. Allelectronics are housed within a weatherproof enclosure (not shown), andpositioned at a low point in the cage.

Air Compressor

An air compressor (not shown) is used to run the pneumatic cylinders(not shown) that open and close the lid and chute door and to provideair to be injected for combustion. The compressor is also used intransporting air through the tubes on the outside of the chamber for theair injection phase in the cycle. The compressor feeds a reservoir tank(not shown) which allows the system to have a certain capacity of storedair. This means that the compressor is not constantly running, whichimproves the life cycle of the unit. The compressor is also housed in asealed enclosure (not shown) to ensure low noise emissions.

Water Pump

A pump is used to move water from a header tank and around the system,feeding components such as the cooling circuit, water jacket and thewater injection feed into the heating chamber (24).

Valves

A network of high spec valves (9, 11, 12, 15) is used to control andthrottle the flow of liquid and gas between the chamber, exhaust,radiator, wet scrubber and purification systems and to enable periodicchange of water in the scrubber. These are controlled remotely by theprogrammable logic controller.

Process Cycle 1. Loading of Waste

The chamber lid is opened and the waste enters the chamber (which is atambient temperature) via the storage chute. The lid is then closed andthe chamber is sealed.

2. Heating

The panel heaters are activated and the interior temperature is raisedto between 500-550° C. The liquid exhaust valve is closed and theemitted gases during the heating phase are passed through the coolingand purification system.

The temperature ramping period takes approximately 5-10 minutes, afterwhich time the temperature is maintained via a thermostat. Due to theefficiency of the chamber insulation the power applied to the heaters isthrottled to maintain the interior chamber temperature.

The gases produced by the waste are monitored and the moisture in thewaste is emitted as a vapour and passed to the exhaust. The mass of afull load of typical waste reduces by approximately 70%.

The temperature is held for approximately 30 minutes.

3. Air Injection (Also Known as the Combustion Phase)

After the heating phase has completed the external panel heaters areturned off and air is passed through the tubes around the outside of thechamber (which preheats the air to a superheated temperatures) andinjected into the top of the chamber. The injectors are such that theair is sprayed as a widely dispersed stream, as opposed to aconcentrated jet. The air is initially pulsed to reduce stress in thesystem, and after a certain period the air is injected constantly.

The flow rate of the air is kept to around 50 l/min (rates of from 25 to100 l/min, and also outside these ranges may be used, depending onsystem size and configuration). This low rate is maintained to ensurethat internal pressure levels within the chamber are not increased toorapidly, as this will compromise the effectiveness of the seals.

With the introduction of air, the waste begins to glow. The volume ofthe waste decreases further, typically reaching around 5% of itsoriginal volume. The waste is converted to a very fine ash.

Smoke and particulate levels in the system increase during the airinjection phase. All gaseous exhausts are passed through the wetscrubber and through the purification system. The combustion phase lastsapproximately 15 minutes.

6. Steam Injection

When the combustion phase has completed the air injection is turned off,the gas exhaust valve is closed, the liquid exhaust valve is opened andwater flows through the same tubes as the air, around the outside of thechamber and is injected as superheated steam. The steam is initiallyinjected in a series of pulses, then as a constant stream. The pulsesare 1 second on, 3 seconds off for 30 pulses, then continuously on for 3minutes. The water is injected at approximately 2 l/min.

The steam both flushes the ash out through to the exhaust, and cleansthe internal faces of the chamber. The steam has a cooling effect on thechamber, and after approximately 1 minute the internal temperature ofthe chamber drops to below 100° C. After the steam injection hascompleted the lid opens and the system is ready for its next cycle. Anyincompatible waste that has not been decomposed by the cycle is held inthe drawer, and can be removed and recycled.

EXAMPLE 1

Apparatus of the invention was tested for its ability to treat domesticwaste whilst ensuring that gas and water emissions did not exceed thelimits imposed by environmental legislation.

A mixed bag of waste was prepared, based on analysis of typicalbreakdown of domestic waste, containing 100 g garden waste, 100 g paperand cardboard, 200 g PVC, 300 g meat by-products and table salt and 100g polyester, making a total weight of 800 g mixed waste.

This mixed waste was treated in apparatus of the invention usingparameters determined to provide waste destruction in a relatively shortperiod of time, these parameters being a pyrolysis temperature of 550°C. for 75 minutes followed by combustion with an air flow of from 40-50litres/min for 15 minutes followed by steam injection to wash the ashresidue into the water collection tank (the tank being used in theemissions test instead of a sewer connection).

This treatment was found to destroy all of the mixed waste, ie. convertit all to ash which was flushed from the chamber with the steam/water.

Testing of the off-gases gave the following results:—

TABLE 1 Off-gas data NO (NOx) SOx HCL mg/m³ mg/m³ mg/m³ EX. 1 6 185 <47Limit stipulated by 400 200 60 environmental legislation

Separately, the wet scrubber water, to be discharged to the sewer innormal operation, was tested for levels of heavy metals and dioxins withthe following results:—

TABLE 2 Off-water Data Thal- Mer- Arse- Cad- Chro- Nick- Diox- lium curynic mium mium Lead el ins Ex. 1 0.002 0.04 38.5 1.4 25.7 125 127 0.01Limit stipulated 0.05 0.03 150 50 500 200 500 0.3 by environ- mentallegisla- tion

Hence, the off-gases and the off-water were inside the emissions limitsstipulated in the environmental legislation.

The invention hence provides treatment of waste by pyrolysis andapparatus for doing so.

1-81. (canceled)
 82. A process for waste treatment comprising:introducing waste into a chamber, heating the waste to an elevatedtemperature to effect pyrolysis of the waste, introducing oxygen intothe chamber to effect combustion of the waste, and flushing thecombusted waste from the chamber with water, wherein the temperature toeffect pyrolysis is from 400-700° C. and the temperature to effectcombustion is at least 400° C.
 83. The process of claim 82, wherein thetemperature to effect pyrolysis is from 500-600° C.
 84. The process ofclaim 83, wherein the temperature to effect pyrolysis is about 550° C.85. The process of claim 82, comprising holding the waste at theelevated temperature for from 10-90 minutes.
 86. The process of claim82, wherein the elevated temperature is held for from 20-60 minutes. 87.The process of claim 82, wherein the elevated temperature is held forfrom 25-40 minutes.
 88. The process of claim 82, comprising holding thewaste at the elevated temperature until 50% or more of the waste isdegraded by pyrolysis.
 89. The process of claim 82, wherein thetemperature to effect combustion is at least 450° C.
 90. The process ofclaim 82, wherein the temperature to effect combustion is at least 500°C.
 91. The process of claim 82, wherein the temperature to effectcombustion is not more than 800° C.
 92. The process of claim 82, whereinthe temperature to effect combustion is not more than 750° C.
 93. Theprocess of claim 82, wherein the temperature to effect combustion is notmore than 700° C.
 94. The process of claim 82, wherein the combustedwaste is flushed through a grid to trap recyclable material.
 95. Theprocess of claim 94, wherein the grid is moveable, and the processfurther comprises moving the grid between a first position in which thegrid traps the recyclable material and a second position in which therecyclable material can be transferred into a receptacle.
 96. Theprocess of claim 82, comprising flushing the combusted waste from thechamber into the sewage system.
 97. The process of claim 82, wherein thewater enters the chamber as superheated steam.
 98. A pyrolysis apparatuscomprising: a sealable chamber, a waste treatment zone in the chamber, aport for introducing waste into the chamber, a port for the exit oftreated waste, a heating element, and a grid between the waste treatmentzone and the exit port, wherein the apparatus is adapted to carry outthe process of claim
 82. 99. The apparatus of claim 98, wherein pipeworkis arranged in the walls of the chamber so that in use water enteringthe chamber is heated by the chamber walls and enters the chamber assuperheated steam.
 100. The apparatus of claim 98, wherein the chambercomprises an output for connection to a sewer so that the treated wastecan be flushed into the sewage system.
 101. The apparatus of claim 98,further comprising a tank to contain a gas treatment solution, anexhaust port for exit of gases from the chamber, and a conduit arrangedin combination with the tank and the exhaust port to contact the gaseswith the solution.